The light emitted by cerium atoms in magnetic fields up to 96,400 oersteds has been photographed at high spectrographic resolution over the range 2500 to 7000A. Interpretable Zeeman patterns of 427 Ce II lines have been reduced, and from them g and J values have been determined for 280 levels. These data have been used to check and extend the classification of Ce II, in which 3600 lines are now assigned to transitions between pairs of 316 levels. The energy system of Ce II consists of two groups of levels which have not yet been connected. Group I is believed to be the lower of the two by approximately 5000 wave numbers. This group consists of levels arising from the electron configurations 4f26s, 4f25d, 4f26p and 4f3. Complete assignments of quantum numbers have been given to all levels in this group on the basis of Zeeman effect studies, combinations, intervals and intensities. All terms have been assigned to electron configurations and parent terms. Group II consists of energy levels believed to originate from the electron configurations 4f5d6s, 4f5d2, 4f5d6p, 4f6s6p, and others. g values to 3 figures after the decimal are well established for many of these levels, but only a few levels are given L and S assignments, which are tentative. Interactions among these levels are strong, and assignment of individual quantum numbers will probably have little significance. Data are now available for complete tests of the g sum rule in a number of cases. It is found to be exact in cases where all perturbing terms are known. g values obtained from different lines for the same energy level are consistent to within 0.003 unit on the average.
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